1. Field of the Invention
The present invention relates to a miniaturization of a loop antenna, and particularly to an antenna device which can be miniaturized by using a grounding conductor.
2. Description of the Related Art
Heretofore, in antenna devices, a miniaturized loop antenna is widely used in which, when a physical size of a one-wavelength loop antenna element 1 shown in FIG. 14 is miniaturized without changing an electrical size thereof, as shown in FIG. 15, a loop antenna element 1a is miniaturized to a half-wavelength by using a grounding conductor 3. One end of this loop antenna element 1a is used as a short-circuit portion 4, and the other end thereof is used as a feed portion 2. The feed portion 2 supplies energy to the grounding conductor 3 via the half-wavelength loop antenna element 1a and the short-circuit portion 4, whereby the length of the loop antenna elment 1a can be reduced substantially to the half physically.
FIG. 16 shows an arrangement of the above-described antenna device in concrete. As shown in FIG. 16, one end of the half-wavelength loop antenna element 1a having substantially U-like shape is connected to the feed portion 2 and the short-circuit portion 4 is connected to the grounding conductor 3. The half-wavelength loop antenna element 1a having substantially U-like shape is made of a linear conductor and is comprised of a third conductor 6 made of a linear conductor formed between two conductors 5L and 5R and disposed parallel to the grounding conductor 3.
The antenna device described with reference to FIG. 16 has the folowing sizes. The length of a linear conductor portion 6a becomes 80 mm and the height of the conductors 5L and 5R become 40 mm even in 800 MHz band which is available in communication via a portable telephone, for example. This antenna device is large in physical size when it is used as an internal antenna device housed in the portable radio receiver or the like whose trend is being reflected on the miniaturization. Hence, this antenna device becomes increasingly difficult to be incorporated within the housing of the portable radio receiver or the like.
An PC card 9 conforming to the standards such as PCMCIA (Personal Computer Memory Card International Association) is inserted into a PC card slot 8 of a notebook size personal computer (hereinafter referred to as a xe2x80x9cnotebook size PCxe2x80x9d) when it is in use as shown in FIG. 17. The PC card is used in other devices such as LAN (Local Area Network) and a portable telephone.
The such PC card 9 includes a radio communication antenna portion 10. When radio communication is executed by using the PC card 9, there is employed an arrangement in which an antenna element 1 is erected from the antenna portion 10 as shown in FIG. 18 or an arrangement in which a meander-like pattern of the antenna element 1 is formed on the card substrate of the antenna portion 10 by patterning as shown in FIG. 19.
However, in the antenna shown in FIG. 18, the antenna should be erected each time the PC card is in use. Moreover, since the antenna is considerably projected to the outside when the PC card 9 is inserted into the notebook size PC 7, there arise problems that portability and operability of the notebook size PC 7 will be deteriorated.
Although the antenna shown in FIG. 19 exhibits satisfactory characteristics in a free space, there is a drawback that, under the condition that the PC card is inserted into the PC card slot 8 of the notebook size PC 7, the antenna portion is easily affected by the notebook size PC 7 and reception sensitivity will be lowered. Moreover, since the antenna portion 10 is considerably projected to the outside when it is inserted into the notebook size PC 7 similarly to the antenna arrangement shown in FIG. 18, there arise problems that portability and operability of the notebook size PC 7 will be degraded.
The present invention is made in order to solve the above-mentioned problems and is to provide an antenna device which can be housed into a suitable means such as a small mobile communication portable telephone housing and a PC card by miniaturizing a loop antenna element comprising the antenna device.
An antenna device according to the present invention is comprised of a first conductor shaped like a nonlinear conductor connected to a feed portion on a grounding conductor and which is disposed in the direction substantially perpendicular to the plane of the grounding conductor, a second conductor shaped like a nonlinear conductor connected to a short-circuit portion of the grounding conductor and which is disposed in the direction substantially perpendicular to the plane of the grounding conductor and a third conductor connecting the first conductor and the second conductor and which is integrally formed in substantially parallel to the grounding conductor, wherein the first and second conductors are shaped like spiral conductors and the third conductor is shaped like a meander conductor.
According to the antenna device of the present invention, the one-wavelength loop antenna can be miniaturized and can be used in a mobile communication portable radio receiver and a PC card.